Calculate positioningArea and not just size, for tiling background.

third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp

Index: third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
diff --git a/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp b/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
index 85cfd59807b1c23ebcbcd70b8d39bdd30037b0da..b99d4c261c8fb26ceab93ca07985b2e888b63a83 100644
--- a/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
+++ b/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
@@ -419,7 +419,7 @@ void BackgroundImageGeometry::calculate(
     const LayoutRect& paintRect) {
   LayoutUnit left;
   LayoutUnit top;
-  LayoutSize positioningAreaSize;
+  LayoutRect positioningArea;
   bool isLayoutView = obj.isLayoutView();
   const LayoutBox* rootBox = nullptr;
   if (isLayoutView) {
@@ -481,8 +481,9 @@ void BackgroundImageGeometry::calculate(
       // The background of the box generated by the root element covers the
       // entire canvas and will be painted by the view object, but the we should
       // still use the root element box for positioning.
-      positioningAreaSize =
-          rootBox->size() - LayoutSize(left + right, top + bottom);
+      positioningArea.setSize(rootBox->size());
+      positioningArea.contractEdges(top, right, bottom, left);
+
       // The input paint rect is specified in root element local coordinate
       // (i.e. a transform is applied on the context for painting), and is
       // expanded to cover the whole canvas.  Since left/top is relative to the
@@ -490,12 +491,14 @@ void BackgroundImageGeometry::calculate(
       left -= paintRect.x();
       top -= paintRect.y();
     } else {
-      positioningAreaSize =
-          (cellUsingContainerBackground
-               ? getBackgroundObjectDimensions(toLayoutTableCell(obj),
-                                               toLayoutBox(positioningBox))
-               : paintRect.size()) -
-          LayoutSize(left + right, top + bottom);
+      if (cellUsingContainerBackground) {
+        positioningArea.setSize(getBackgroundObjectDimensions(
+            toLayoutTableCell(obj), toLayoutBox(positioningBox)));
+      } else {
+        positioningArea = paintRect;
+      }
+
+      positioningArea.contractEdges(top, right, bottom, left);
     }
   } else {
     setHasNonLocalGeometry();
@@ -517,11 +520,11 @@ void BackgroundImageGeometry::calculate(
           LayoutPoint(-paintContainer->localToAbsolute(FloatPoint())));
 
     setDestRect(viewportRect);
-    positioningAreaSize = destRect().size();
+    positioningArea = viewportRect;
   }
 
   LayoutSize fillTileSize(
-      calculateFillTileSize(positioningBox, fillLayer, positioningAreaSize));
+      calculateFillTileSize(positioningBox, fillLayer, positioningArea.size()));
   // It's necessary to apply the heuristic here prior to any further
   // calculations to avoid incorrectly using sub-pixel values that won't be
   // present in the painted tile.
@@ -530,12 +533,10 @@ void BackgroundImageGeometry::calculate(
   EFillRepeat backgroundRepeatX = fillLayer.repeatX();
   EFillRepeat backgroundRepeatY = fillLayer.repeatY();
   LayoutUnit unsnappedAvailableWidth =
-      positioningAreaSize.width() - fillTileSize.width();
+      positioningArea.width() - fillTileSize.width();
   LayoutUnit unsnappedAvailableHeight =
-      positioningAreaSize.height() - fillTileSize.height();
-  positioningAreaSize =
-      LayoutSize(snapSizeToPixel(positioningAreaSize.width(), m_destRect.x()),
-                 snapSizeToPixel(positioningAreaSize.height(), m_destRect.y()));
+      positioningArea.height() - fillTileSize.height();
+  LayoutSize positioningAreaSize(positioningArea.pixelSnappedSize());

[Stephen Chennney, 2017/03/01 14:48:29]

This is a subtle change that might change snapping because we're no longer
trying to snap the same way that the dest rect will snap (or something like
that). Is your change in behavior deliberate? If not, leave it in the old format
in this case.

[Karl Øygard, 2017/03/03 15:00:07]

Good catch, this does not belong here.  Thanks!

   LayoutUnit availableWidth = positioningAreaSize.width() - tileSize().width();
   LayoutUnit availableHeight =
       positioningAreaSize.height() - tileSize().height();